Co-fired capacitor and method for forming ceramic capacitors for use in printed wiring boards

ABSTRACT

A capacitor structure is fabricated by forming a pattern of first dielectrics over a foil, forming first electrodes over the first dielectrics, and co-firing the first dielectrics and the first electrodes. Co-firing of the dielectrics and the electrodes alleviates cracking caused by differences in thermal coefficient of expansion (TCE) between the electrodes and the dielectrics. Co-firing also ensures a strong bond between the dielectrics and the electrodes. In addition, co-firing allows multi-layer capacitor structures to be constructed, and allows the capacitor electrodes to be formed from copper.

BACKGROUND

[0001] 1. Technical Field

[0002] The technical field is ceramic capacitors. More particularly, thetechnical field includes co-fired ceramic capacitors that may beembedded in printed wiring boards.

[0003] 2. Background Art

[0004] Passive circuit components embedded in printed wiring boardsformed by fired-on-foil technology are known. Known components areseparately fired-on-foil. “Separately fired-on-foil” capacitors areformed by depositing a thick-film dielectric material layer onto ametallic foil substrate and firing under thick-film firing conditions,and subsequently depositing a top electrode material over the thick-filmdielectric material layer. U.S. Pat. No. 6,317,023 B1 to Feltendiscloses such a process.

[0005] The thick-film dielectric material should have a high dielectricconstant (K) after firing. A high K thick-film dielectric is formed bymixing a high dielectric constant K powder (the “functional phase”) witha glass powder and dispersing the mixture into a thick-filmscreen-printing vehicle. High K glasses can be wholly or partiallycrystalline, depending on their composition and the amount of high Kcrystal they precipitate. These glasses are often termed“glass-ceramics.”

[0006] During firing of the thick-film dielectric material, the glasscomponent of the dielectric material softens and flows before the peakfiring temperature is reached, coalesces, encapsulates the functionalphase, and subsequently crystallizes, forming the glass-ceramic. Theglass-ceramic, however, does not re-soften and flow on subsequentfirings, and its surface is often difficult to adhere to.

[0007] Silver and silver-palladium alloys are preferred metals forforming capacitor electrodes because of their relatively smalldifferences in thermal coefficient of expansion (TCE) from thedielectrics used in fired-on-foil capacitors. Small TCE differencesresult in low stress in the electrode upon cooling from peak firingtemperatures. However, silver and silver-containing alloys may beundesirable in some applications because of the possibility of silvermigration. In addition, the relatively low melting points of silver andsilver alloys preclude their use at higher firing temperatures.

[0008] Copper is a preferred material for forming electrodes, but thelarge TCE differences between copper and thick-film capacitordielectrics lead to post-firing stresses in the electrodes. The stressesresult in electrode cracking. In addition, because pre-fired glassceramics do not re-soften and flow on subsequent firings, a copperelectrode fired on a pre-fired glass-ceramic surface may not adhere wellto the glass-ceramic. The electrode may therefore separate from thedielectric. Both cracking and separation result in high dissipationfactors.

SUMMARY

[0009] According to a first embodiment, a method for making afired-on-foil ceramic capacitor structure comprises forming firstdielectrics over a metallic foil, forming first electrodes over thefirst dielectrics, and co-firing the first dielectrics and the firstelectrodes. In the first embodiment, cracking and separation of theelectrode from the dielectric caused by differences in thermalcoefficient of expansion (TCE) between the electrodes and thedielectrics is avoided by co-firing the electrodes and the dielectrics.Alleviation of the TCE problem also allows the use of preferredmaterials, such as copper, to form the electrodes.

[0010] According to a second embodiment, a two-layer capacitor structurecomprises a metallic foil, dielectrics disposed over the foil, firstelectrodes disposed over the first dielectrics, and second electrodesdisposed over the dielectrics and over the first electrodes. In thesecond embodiment, the capacitance density of the capacitor structure isincreased because of the additional dielectric/electrode layer.Additional layers may also be added, further increasing capacitancedensity. Also according to the second embodiment, the capacitorstructure may comprise a copper foil and copper electrodes.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The detailed description will refer to the following drawings,wherein like numerals refer to like elements, and wherein:

[0012]FIGS. 1A to 1D schematically illustrate steps in manufacturing afirst embodiment of a capacitor structure shown in front elevation;

[0013]FIG. 1E is a top plan view of the first capacitor structureembodiment;

[0014]FIGS. 2A to 2J schematically illustrate steps in manufacturing asecond embodiment of a capacitor structure shown in front elevation;

[0015]FIG. 2K is a top plan view of the second capacitor structureembodiment; and

[0016]FIG. 3 illustrates a third embodiment of a capacitor structure.

DETAILED DESCRIPTION

[0017] FIGS. 1A-1D illustrate a general method of manufacturing acapacitor structure 100 (FIG. 1E) having a single-layer capacitor onmetallic foil design. FIG. 1E is a plan view of the finished capacitorstructure 100. Specific examples of the capacitor structure 100 are alsodescribed below.

[0018]FIG. 1A is a side elevational view of first stage of manufacturingthe capacitor structure 100. In FIG. 1A, a metallic foil 110 isprovided. The foil 110 may be of a type generally available in theindustry. For example, the foil 110 may be copper, copper-invar-copper,invar, nickel, nickel-coated copper, or other metals that have meltingpoints in excess of the firing temperature for thick film pastes.Preferred foils include foils comprised predominantly of copper, such asreverse treated copper foils, double-treated copper foils, and othercopper foils commonly used in the multilayer printed circuit boardindustry. The thickness of the foil 110 may be in the range of, forexample, about 1-100 microns, preferably 3-75 microns, and mostpreferably 12-36 microns, corresponding to between about ⅓ oz and 1 ozcopper foil.

[0019] The foil 110 may be pretreated by applying an underprint 112 tothe foil 110. The underprint 112 is a relatively thin layer applied to acomponent-side surface of the foil 110. In FIG. 1A, the underprint 112is indicated as a surface coating on the foil 110. The underprint 112adheres well to the metal foil 110 and to layers deposited over theunderprint 112. The underprint 112 may be formed, for example, from apaste applied to the foil 110, and is then fired at a temperature belowthe softening point of the foil 110. The paste may be printed as an opencoating over the entire surface of the foil 110, or printed on selectedareas of the foil 110. It is generally more economical to print theunderprint paste over selected areas of the foil. When a copper foil 110is used in conjunction with a copper underprint 112, glass in the copperunderprint paste retards oxidative corrosion of the copper foil 110, andit may therefore be preferable to coat the entire surface of the foil110 if oxygen-doped firing is utilized.

[0020] In FIG. 1A, a dielectric material is screen-printed onto thepretreated foil 110, forming a first dielectric layer 120. Thedielectric material may be, for example, a thick-film dielectric ink.The dielectric ink may be formed of, for example, a paste. The firstdielectric layer 120 is then dried. In FIG. 1B, a second dielectriclayer 125 is then applied, and dried. In an alternative embodiment, asingle layer of dielectric material may be deposited through a coarsermesh screen to provide an equivalent thickness in one printing.

[0021] In FIG. 1C, an electrode 130 is formed over the second dielectriclayer 125 and dried. The electrode 130 can be formed by, for example,screen-printing a thick-film metallic ink. In general, the surface areaof the dielectric layer 125 should be larger than that of the electrode130.

[0022] The first dielectric layer 120, the second dielectric layer 125,and the electrode 130 are then co-fired. The thick-film dielectriclayers 120, 125 may be formed of, for example, a high dielectricconstant functional phase such as barium titanate and a dielectricproperty-modifying additive such as zirconium dioxide, mixed with aglass-ceramic frit phase. During co-firing, the glass-ceramic frit phasesoftens, wets the functional and additive phases and coalesces to createa dispersion of the functional phase and the modifying additive in aglass-ceramic matrix. At the same time, the copper electrode powders ofthe layer 130 are wetted by the softened glass-ceramic frit phase andsinter together to form a solid electrode. The layer 130 has a strongbond to the high K dielectric 128 that results from the co-firing. Thepost-fired structure is shown in front elevation in FIG. 1D.

[0023]FIG. 1E is a plan view of the finished capacitor structure 100. InFIG. 1E, four dielectric/electrode stacks 140 on the foil 110 areillustrated. Any number of stacks 140, in various patterns, however, canbe arranged on a foil 110 to form the capacitor structure 100.

[0024] Examples 1-3 illustrate particular materials and processes usedin practicing the general method illustrated by FIGS. 1A-1E.

[0025] FIGS. 2A-2J illustrate a method of manufacturing a capacitorstructure 200 having a double-layer capacitor on metallic foil design.FIG. 2K is a plan view of the finished capacitor structure 200.

[0026]FIG. 2A is a front elevational view of first stage ofmanufacturing the capacitor structure 200. In FIG. 2A, a metallic foil210 is provided. The foil 210 may be pretreated by applying and firingan underprint 212, as discussed above with reference to FIG. 1A. Adielectric material is screen-printed onto the pretreated foil 210,forming a first dielectric layer 220. The first dielectric layer 220 isthen dried.

[0027] In FIG. 2B, a second dielectric layer 225 is then applied, anddried. A single layer of dielectric material may alternatively be used.

[0028] In FIG. 2C, a first electrode 230 is formed over the seconddielectric layer 225 and dried. The first electrode may be formed by,for example, screen-printing a thick-film metallic ink. The firstelectrode 230 is formed to extend to contact the foil 210.

[0029] The first dielectric layer 220, the second dielectric layer 225,and the first electrode 230 are then co-fired. The dielectric layers220, 225 may have similar compositions to the materials discussed abovewith reference to FIGS. 1A-1E, and the co-firing process imparts theadvantages of adhesion and defect-free processing discussed above. Aresulting dielectric 228 is formed from the co-firing step, as shown inFIG. 2D.

[0030] In FIG. 2E, a third layer of dielectric material isscreen-printed onto the co-fired structure of FIG. 2D, forming a thirddielectric layer 240. The third dielectric layer 240 is then dried. InFIG. 2F, a fourth dielectric layer 245 is applied and dried. A singlelayer of dielectric material may alternatively be used.

[0031] In FIG. 2G, a second electrode 250 is formed over the fourthdielectric layer 245 and dried. The second electrode 250 extends tocontact the foil 210. The structure is then co-fired. FIG. 2Hillustrates the structure after co-firing, with the resulting dielectric260 and dielectric/electrode stack 265. After co-firing, the dielectric260 securely adheres to both electrodes 230, 250, and the electrodes230, 250 are crack-free.

[0032] As an alternative to two separate firing steps as discussed withreference to FIGS. 2D and 2H, a single co-firing can be performed afterforming the second electrode 250. A single co-firing is advantageous inthat production costs are reduced. Two separate firings, however, allowinspection of the first electrode 230 for defects such as cracks and forprinting alignment issues after the first firing.

[0033] In FIG. 21, the structure may be inverted and laminated. Forexample, the component face of the foil 210 can be laminated withlaminate material 270. The lamination can be performed, for example,using FR4 prepreg in standard printing wiring board processes. In oneembodiment, 106 epoxy prepreg may be used. Suitable laminationconditions are 185° C. at 208 psi for 1 hour in a vacuum chamberevacuated to 28 inches of mercury. A silicone rubber press pad and asmooth PTFE filled glass release sheet may be in contact with the foil210 to prevent the epoxy from gluing the lamination plates together. Afoil 280 may be applied to the laminate material 270 to provide asurface for creating circuitry. The embodiments of the capacitorstructure 100 discussed above with reference to FIG. 1E may also belaminated in this manner. The dielectric prepreg and laminate materialscan be any type of dielectric material such as, for example, standardepoxy, high Tg epoxy, polyimide, polytetrafluoroethylene, cyanate esterresins, filled resin systems, BT epoxy, and other resins and laminatesthat provide insulation between circuit layers.

[0034] Referring to FIG. 2J, after lamination, a photo-resist is appliedto the foil 210 and the foil 210 is imaged, etched and stripped usingstandard printing wiring board processing conditions. The etchingproduces a trench 215 in the foil 210, which breaks electrical contactbetween the first electrode 230 and the second electrode 250. FIG. 2K isa top plan view of the completed capacitor structure 200. A section 216of the foil 210 is one electrode of the resulting capacitor structure200, and may be connected to other circuitry by a conductive trace 218.A section 227 is coupled to the second electrode 230 and may beconnected to other circuitry by a conductive trace 219.

[0035] The capacitor structure 200 discussed above has high capacitancedensity due to its two-layer capacitor structure. In addition, thecapacitor structure 200 can be produced crack-free by co-firing of thedielectric layers and the electrodes.

[0036]FIG. 3 illustrates a third embodiment of a capacitor structure.The capacitor structure 300 is a three-layer embodiment having a highcapacitance density. The capacitor structure 300 comprises a foil 310and a plurality of dielectric/electrode stacks 365 (only one stack 365is illustrated). The dielectric/electrode stack 365 include a firstelectrode 330 and a second electrode 350 separated by a dielectric 360,similar to the first and second electrodes 230, 250 of the capacitorstructure 200 discussed above. Each dielectric/electrode stack 365 alsohas a third electrode 335 formed over the dielectric 360. A trench 315breaks electrical contact of a portion 316 of the foil 310 and theelectrode 350, from a portion 317 of the foil 310, the first electrode330, and the third electrode 335. A laminate material 370 and a secondfoil 380 may be included in the capacitor structure 300.

[0037] The capacitor structure 300 can be manufactured in a mannersimilar to the capacitor structure 200. The third layer portion of thedielectrics 360 in the stacks 365 may be formed from one or moredielectric ink layers, as discussed above, and the electrodes 335 can beformed over the dielectrics 360.

[0038] The dielectric/electrode stacks 365 can be co-fired in threeindividual steps, or in a single step. Firing of eachelectrode/dielectric layer allows inspection of the product for defects.A single firing, however, reduces the cost of producing the capacitorstructure 300.

[0039] The additional layer in the dielectric/electrode stacks 365provides a high capacitance density for the capacitor structure 300.Co-firing of the dielectric layers and the electrode provides a lowdissipation factor and crack-free structure.

[0040] In other embodiments, four or more layer capacitor structures canbe produced by alternatively forming dielectric and electrode layers,and co-firing the layers.

[0041] In the embodiments discussed in this specification, the term“paste” may correspond to a conventional term used in the electronicmaterials industry, and generally refers to a thick-film composition.Typically, the metal component of the underprint paste is matched to themetal in the metal foil. For example, if a copper foil were used, then acopper paste could be used as the underprint. Examples of otherapplications would be pairing silver and nickel foils with a similarmetal underprint paste. Thick film pastes may be used to form both theunderprint and the passive components.

[0042] Generally, thick-film pastes comprise finely divided particles ofceramic, glass, metal or other solids dispersed in polymers dissolved ina mixture of plasticizer, dispersing agent and organic solvent.Preferred capacitor pastes for use on copper foil have an organicvehicle with good burnout in a nitrogen atmosphere. Such vehiclesgenerally contain very small amounts of resin, such as high molecularweight ethyl cellulose, where only small amounts are necessary togenerate a viscosity suitable for screen-printing. Additionally, anoxidizing component such as barium nitrate powder, blended into thedielectric powder mixture, helps the organic component burn out in thenitrogen atmosphere. Solids are mixed with an essentially inert liquidmedium (the “vehicle”), then dispersed on a three-roll mill to form apaste-like composition suitable for screen-printing. Any essentiallyinert liquid may be used as the vehicle. For example, various organicliquids, with or without thickening and/or stabilizing agents and/orother common additives, may be used as the vehicle.

[0043] High K thick-film dielectric pastes generally contain at leastone high K functional phase powder and at least one glass powderdispersed in a vehicle system composed of at least one resin and asolvent. The vehicle system is designed to be screen-printed to providea dense and spatially well-defined film. The high K functional phasepowders can comprise perovskite-type ferroelectric compositions with thegeneral formula ABO₃. Examples of such compositions include BaTiO₃;SrTiO₃; PbTiO₃; CaTiO₃; PbZrO₃; BaZrO₃ and SrZrO₃ Other compositions arealso possible by substitution of alternative elements into the A and/orB position, such as Pb(Mg_(1/3)Nb_(2/3))O₃ and Pb(Zn_(1/3)Nb_(2/3))O₃.TiO₂ and SrBi₂Ta₂O₉ are other possible high K materials.

[0044] Doped and mixed metal versions of the above compositions are alsosuitable. Doping and mixing is done primarily to achieve the necessaryend-use property specifications such as, for example, the necessarytemperature coefficient of capacitance (TCC) in order for the materialto meet industry definitions, such as “X7R” or “Z5U” standards.

[0045] The glasses in the pastes can be, for example, Ca—Alborosilicates, Pb—Ba borosilicates, Mg—Al silicates, rare earth borates,and other similar glass compositions. High K glass-ceramic powders, suchas lead germanate (Pb₅Ge₃O₁₁), are preferred.

[0046] Pastes used to form the electrode layers may be based on metallicpowders of either copper, nickel, silver, silver-containing preciousmetal compositions, or mixtures of these compounds. Copper powdercompositions are preferred.

[0047] The capacitor structure embodiments described in thisspecification have many applications. For example, the capacitorstructure embodiments can be used within organic printed circuit boards,IC packages, applications of said structures in decoupling applications,and devices such as IC modules or handheld device motherboards.

[0048] In the above embodiments, the electrode layers are described asformed by screen-printing. Other methods, however, such as deposition bysputtering or evaporation of electrode metals onto the dielectric layersurface may also be used.

[0049] The foregoing description of the invention illustrates anddescribes the present invention. Additionally, the disclosure shows anddescribes only the preferred embodiments of the invention, but it is tobe understood that the invention is capable of use in various othercombinations, modifications, and environments and is capable of changesor modifications within the scope of the inventive concept as expressedherein, commensurate with the above teachings, and/or the skill orknowledge of the relevant art. The embodiments described hereinabove arefurther intended to explain best modes known of practicing the inventionand to enable others skilled in the art to utilize the invention insuch, or other, embodiments and with the various modifications requiredby the particular applications or uses of the invention. Accordingly,the description is not intended to limit the invention to the formdisclosed herein. Also, it is intended that the appended claims beconstrued to include alternative embodiments.

EXAMPLES Example 1

[0050] Referring to FIGS. 1A-1E, a specific embodiment of the capacitorstructure 100 was described. In this embodiment, the foil 110 was acopper foil. The type of copper foil 110 can be any commercial grade ofcopper foil used in the printed wiring board industry, and may be in therange of ⅓ oz copper foil (approximately 12 microns thickness) to 1 ozcopper foil (approximately 36 microns thickness). The copper foil 110was pretreated by applying a copper underprint paste over selected areasof the foil 110. The resulting product was then fired in nitrogen at900° C. for 10 minutes at peak temperature, with a total cycle time ofapproximately 1 hour, forming the underprint 112.

[0051] In FIG. 1B, a thick-film dielectric ink was screen-printed ontothe pretreated copper foil 110 through 400 mesh screen to create apattern of ½ inch by ½ inch first dielectric layers 120. The wet printedthickness of the first dielectric layers 120 is approximately 12-15microns. The first dielectric layers 120 were dried at 125° C. forapproximately 10 minutes, and second dielectric layers 125 were appliedby screen-printing, followed by another drying step at 125° C. Thethick-film dielectric ink included a barium titanate component, azirconium oxide component, and a glass-ceramic phase.

[0052] Referring to FIG. 1C, thick-film copper electrode ink layers 130was printed through 400 mesh screens onto the dielectric squares 120,and dried at 125° C. for approximately 10 minutes to form a 0.9 cm by0.9 cm square electrode. In general, the printed electrode 130 thicknesswas limited only by the need for a pinhole-free film, and was typicallyin the range of 3 to 15 microns. The resulting structure was co-fired to900° C. for 10 minutes at peak temperature using a thick film nitrogenprofile. The nitrogen profile included less than 50 ppm oxygen in theburnout zone, and 2-10 ppm oxygen in the firing zone, with a total cycletime of 1 hour. Co-firing resulted in the dielectric/electrode stacks140 illustrated in FIG. 1E.

[0053] In this example, the thick film dielectric material had thefollowing composition: Barium titanate powder 64.18% Zirconium oxidepowder  3.78% Glass A 11.63% Ethyl cellulose  0.86% Texanol 18.21%Barium nitrate powder  0.84% Phosphate wetting agent  0.5%. Glass Acomprised: Germanium oxide  21.5% Lead tetraoxide  78.5%.

[0054] The Glass A composition corresponded to Pb₅Ge₃O₁₁, whichprecipitated out during the firing, and had a dielectric constant ofapproximately 70-150. The thick film copper electrode ink comprised:Copper powder 55.1% Glass A  1.6% Cuprous oxide powder  5.6% Ethylcellulose T-200  1.7% Texanol 36.0%.

[0055] After firing, the capacitor structure was crack free and had thefollowing electrical characteristics: capacitance density approximately150 nF/in² dissipation factor approximately 1.5% insulationresistance >5 × 10⁹ Ohms breakdown voltage approximately 800 volts/mil.

[0056] In this example, the use of copper as the material to form thefoil 110 and the electrodes 130 was advantageous because copper was notsubject to a large degree of migration. In conventional, separatelyfired-on-foil methods, the large TCE difference between copper anddielectric materials leads to cracking and separation of the electrodefrom the dielectric, and high dissipation factors. However, by co-firingthe electrodes and dielectrics, cracking did not occur and lowdissipation factors were achieved.

Example 2

[0057] A process as described in Example 1 was repeated, except that thethick-film dielectric 128 was printed through 325 mesh screen, with awet thickness of each of the two layers of approximately 15-20 microns.Results were similar to the embodiment of Example 1, except that thecapacitance density was approximately 120 nF/inch².

Example 3

[0058] A process as described in Example 2 was repeated using a varietyof dielectric and electrode dimensions shown in the table below:Dielectric Electrode Dielectric Electrode Size mils Size mils Size milsSize mils 250 × 250 210 × 210  36 × 338  20 × 320  56 × 340  40 × 320 96 × 340  80 × 320 176 × 340 160 × 320  36 × 178  20 × 157  96 × 180 80 × 158 336 × 180 320 × 158  26 × 180  10 × 159  56 × 180  40 × 158176 × 180 160 × 158  26 × 100 10 × 74 36 × 98 20 × 77  56 × 100 40 × 78 56 × 100 40 × 78  96 × 100 80 × 78 176 × 100 160 × 78  26 × 60 10 × 3936 × 58 20 × 37 56 × 60 40 × 38 96 × 60 80 × 38 26 × 40 10 × 18 36 × 3816 × 17 56 × 40 40 × 18 26 × 30 10 × 9  36 × 28 20 × 7   26 × 340  10 ×318 336 × 340 320 × 318 90 × 90 70 × 70 170 × 170 150 × 150 330 × 330310 × 310 240 × 240 229.5 × 229.5 119.5 × 119.5 109.5 × 109.5

[0059] Capacitance in these embodiments was proportional to the area ofthe printed copper electrode, but the calculated capacitance densitieswere essentially identical to that of Example 1.

What is claimed is:
 1. A method for making a fired-on-foil capacitorstructure, comprising: providing a metallic foil; forming at least onefirst dielectric over the foil; forming at least one first electrodeover the first dielectric; and co-firing the first dielectric and thefirst electrode.
 2. The method of claim 1, wherein forming the firstelectrode comprises: forming the first electrode comprising a metal,wherein the metallic foil also comprises the metal.
 3. The method ofclaim 2, wherein the metal is copper.
 4. The method of claim 1,comprising: forming at least one second dielectric over the firstelectrode; and forming at least one second electrode over the seconddielectric.
 5. The method of claim 4, comprising: co-firing the seconddielectric and the second electrode.
 6. The method of claim 4, whereinco-firing comprises: co-firing the second dielectric and the secondelectrode along with the first dielectric and the first electrode. 7.The method of claim 4, comprising: forming a trench in the foil toelectrically isolate the first and second electrodes.
 8. The method ofclaim 4, comprising: laminating a side of the foil containing the firstdielectric and the first electrode.
 9. The method of claim 4,comprising: forming at least one third dielectric over the secondelectrode; and forming at least one third electrode over the thirddielectric.
 10. The method of claim 9, comprising: co-firing the thirddielectric and the third electrode.
 11. The method of claim 9, whereinco-firing comprises: co-firing the third dielectric and the thirdelectrode along with the first and second dielectrics and the first andsecond electrodes.
 12. The method of claim 9, comprising: forming atrench in the foil to electrically isolate the first and thirdelectrodes from the second electrode.
 13. The method of claim 1, whereinproviding a foil comprises: treating the foil with an underprint; andfiring at a temperature below the softening point of the foil.
 14. Themethod of claim 1, wherein forming the first dielectric comprises:screen-printing a layer of dielectric ink over the foil; and drying thedielectric ink.
 15. The method of claim 14, wherein forming the firstelectrode comprises: screen-printing a layer of metallic ink over thefirst dielectric; and drying the metallic ink.
 16. The method of claim1, wherein: forming at least one first dielectric comprises forming apattern of a plurality of first dielectrics over the foil; and formingat least one first electrode comprises forming a pattern of a pluralityof first electrodes over the first dielectrics.
 17. A capacitorstructure, comprising: a metallic foil; at least one dielectric disposedover the foil; at least one first electrode disposed over a portion ofthe dielectric; and at least one second electrode disposed over aportion of the dielectric and over a portion of the first electrode,wherein a portion of the dielectric is disposed between the first andsecond electrodes.
 18. The capacitor structure of claim 17, wherein thefoil comprises: a trench that electrically isolates the first electrodefrom the second electrode.
 19. The capacitor structure of claim 17,wherein: the at least one dielectric comprises a plurality ofdielectrics; the at least one first electrode comprises a plurality offirst electrodes; the at least one second electrode comprises aplurality of second electrodes; and the dielectrics, the firstelectrodes, and the second electrodes are arranged as a plurality ofstacks on the metallic foil, each stack comprising a first electrode, asecond electrode, and a dielectric.
 20. The capacitor structure of claim19, comprising: a plurality of third electrodes, one in each stack,wherein each third electrode is disposed over a portion of acorresponding dielectric and over a portion of a corresponding firstelectrode and is electrically connected to the corresponding firstelectrode.
 21. The capacitor structure of claim 19, wherein the metallicfoil and the first and second electrodes comprise copper.